1. Field of the Invention
This invention relates to steel trusses and joists comprising parallel flanges extending orthogonally from web sides, and more particularly to a truss or a joist with at least one slot in the web or primary flanges and including supplemental flanges extending from slot sides.
2. Prior Art
Interior wall construction using horizontal channel beams as headers and footers and matching vertical studs received into the channel beams is well-known. Commonly, the studs are also channel-shaped and both are made of metal, typically cold formed metal and more typically steel. Similarly, metal buildings employ girts (sidewall bracing) and perlins (roof bracing). Roof rafters, headers, footers, beams, and joists and trusses comprised of a plurality of similar elongate components can also employ channel shaped members. All of these building components have in common that they are elongate and straight, including the truss comprising a plurality of elongate building components. For purposes of simplicity of description, they are collectively referred to as a “beam” unless otherwise indicated in the context. That is, for purposes herein, the description referencing a beam should be deemed to include and apply to each and all elongate building components, specifically including those listed and also including the elongate building components of which a truss is comprised. For purposes herein, reference may be made to metal or steel beam. These terms are not meant to be restrictive or limitations but are meant illustratively and generically to be synonymous and to include all materials from which such studs may be formed.
Of all modes of failure, buckling (Euler or local) is probably the most common and most catastrophic. That is, a structure may fail to support a load when a member in compression buckles, that is, moves laterally and shortens in length. A steel beam may be described for these purposes as a slender column where its length is much greater than its cross-section. Euler's equations show that there is a critical load for buckling of a slender column. With a large load exceeding the critical load, the least disturbance causes the column to bend sideways, as shown in the inserted diagram, which increases its bending moment. Because the bending moment increases with distance from a vertical axis, the slight bend quickly increases to an indefinitely large transverse displacement within the column; that is, it would buckle. This means that any buckling encourages further buckling and such failure becomes catastrophic.
The traditional steel beam construction comprises a pair of parallel flanges extending orthogonally from a web. Commonly the flange distal end bends inward slightly to increase the compressive stability converting the flat two-dimensional flange into a three dimensional structure. For these purposes, “compressive stability, strength or stress” means a reference value that measures the load a structure can sustain before it buckles or otherwise deforms and loses support for a load.
Such beams are very poor energy conservers. For example, for internal walls the metal beam acts as a thermal conduit and actually enhances thermal conductivity across the wall over wood and other materials. In metal buildings the beams (girts and perlins) are in direct metal-to-metal contact with the outside material sheeting and become conduits of heat on the outside sheeting to inside the building. Heat passes through the web, so one interested in reducing thermal conductive might consider removing material from the web to create slots in the web. To the extent such slots remove metal and thus reduce the thermal path, the beam is less conductive thermally. Also, such slots may receive insulation that further impede conductivity.
Similarly, a steel beam is a good acoustic conductor, which is detrimental in many applications. It has long been desired to reduce sound transmission through metal wall beams. As in thermal conductivity, re-shaping of a significant portion of the web or the flanges will reduce the acoustic conductivity of the beam and therefore the wall.
It is a primary object of the present invention to enhance the compressive stability, strength and bending resistance of a traditional steel beam. It is another object to reduce thermal conductivity and acoustical transmission, of the beam while enhancing the bending resistance and compressive stability and strength. To this end, it is a further object to introduce one or more slots in the beam web that interrupt conductivity across the web in combination with projections from the web at the slots additional to the primary flanges that enhance the load that a beam can support under bending and compression.